1. Field of the Invention
The present invention relates to improved elastomer films, particularly heat-shrinkable films, which are used for a variety purposes including the formation of elastic waistband portions of disposable diapers.
2. Discussion of Prior Art
Diapers are produced from a variety of different plastic films which are used to form different portions of the diaper. The films used to form the main portions, or backsheets of the diaper are inexpensive non-elastomer thermoplastic films such as olefin homopolymers. Such thermoplastic films conventionally are embossed during extrusion, but are not oriented, elastomeric or heat-shrinkable. Reference is made to U.S. Pat. Nos. 4,436,520 and 4,668,463 for their disclosure of embossing such films during extrusion.
Elastomer films are used to form small areas of disposable diapers, i.e., areas such as waistbands and legbands, where elastic properties are advantageous to improve the fit of the diaper. Such films generally are oriented or stretched to impart the desired degree of heat-shrinkability thereto so that shrinking occurs upon heat application.
Elastomer films generally present high blocking problems since they contain adhesive polymers such as ethylene-vinyl acetate (EVA) and/or rubbers and oily plasticizers. Therefore it is known to extrude such films against sandblasted embossing rolls to form a random micropattern embossment on a surface thereof to reduce the blocking tendencies of the film, whereby it can be rolled or fed more easily to the tentering station for orienting or stretching in the machine direction (MD) and/or transverse direction (TD). However, the orientation draws down and substantially reduces the random surface embossment so that normal high blocking properties reappear. The high blocking properties make it difficult to handle the film downstream of the tentering station, and most difficult to unwind the elastomer film after it has been collected on a roll.
It is known from U.S. Pat. Nos. 4,848,564 to extrusion-emboss thermoplastic films such as polyethylene, and elastomeric films such as copolymers of ethylene and vinyl acetate (EVA) or other co-monomers, using either a sandblasted or random micro-roughened embossing roll, or an embossing roll having its surface engraved with a geometric micro pattern having an embossed depth from 0.0005 "to 0.0025", such geometric-embossed rolls being described in U.S. Pat. No. 4,367,147.
The films of U.S. Pat. No. 4,848,564 are embossed in order to improve their non-blocking or release properties with respect to rubber bales on which they are used as wrappers. The embossed films of the patent are not oriented or stretched.